Isotopes fission product

Uranium-239 [13982-01 -9] has a half-life of 23.5 min neptunium-239 [13968-59-7] has a half-life of 2.355 d. Recycling or reprocessing of spent fuel involves separation of plutonium from uranium and from bulk fission product isotopes (see Nuclearreactors, chemical reprocessing). 

The primary issue is to prevent groundwater from becoming radioactively contaminated. Thus, the property of concern of the long-lived radioactive species is their solubility in water. The long-lived actinides such as plutonium are metallic and insoluble even if water were to penetrate into the repository. Certain fission-product isotopes such as iodine-129 and technicium-99 are soluble, however, and therefore represent the principal although very low level hazard. Studies of Yucca Mountain, Nevada, tentatively chosen as the site for the spent fuel and high level waste repository, are underway (44). 

SLIDER is a Fortran IV computer program for investigating the diffusion of a single fission-product isotope in a multilayered spherical fuel particle. This code enables one to compute, on the basis of Fick s law of diffusion, the transient and steady-state fission product concentrations and releases in multilayered spherical geometry. 

Values a and b for the fission product isotopes and the partition factors ai and a2 are listed in Table V au for a given isotope, is the fraction which was retained by the local fallout glass particles, and < > is the fraction released to the cloud. Thus, from Table V, i137 is 0.153 which indicates that 15.3% of the 137Cs is retained by the local glass particles. It is interesting to note that the independent yield of cesium in the 137 mass chain is approximately 17%—the balance of the chain is formed as tellurium, iodine, and xenon. 

Table 2.4 shows the activities of fission products, relative to 137Cs, in the reactor fuel, the stack filter and sampling filters in the environment. All the environmental samples showed activity of the relatively volatile fission products, isotopes of Te, I and Cs, and only traces of the refractory elements, such as Zr, the rare earths and the alkaline earths. 

There was a progressive reduction in the activities relative to Cs of the refractory fission products, isotopes of Zr and Ce (boiling points 4400 and 2900°C), with increasing distance from Chernobyl. Ru is also refractory, but its oxide Ru04 is relatively volatile, and Ru was more persistent in long-range travel. 

Radiometric techniques, essentially alpha and gamma spectrometry, allow the determination of a number of fissile and fission product isotopes. 

Irradiated uranium fuel elements contain fission product isotopes, activation products produced by atoms exposed to the intense neutron, ot, (3, and y radiation in the reactor core, and actinides, produced by neutron capture of the nuclei of atoms with atomic... 

In addition to fissionable isotopes ( U, or plutonium) and fertile isotopes ( U or thorium), spent fuel from a reactor contains a large number of fission product isotopes, in which all elements of the periodic table from zinc to gadolinium are represented. Some of these fission product isotopes are short-lived and decay rapidly, but a dozen or more need to be considered when designing processes for separation of reactor products. The most important neutron-absorbing and long-lived fission products in irradiated uranium are listed in Table 1.4. 

Once the radioactive fission products are isolated by one of the separation processes, the major problem in the nuclear chemical industry must be faced since radioactivity cannot be immediately destroyed (see Fig. 10-7c for curie level of fission-product isotopes versus elapsed time after removal from the neutron source). This source of radiation energy can be employed in the food-processing industries for sterilization and in the chemical industries for such processes as hydrogenation, chlorination, isomerization, and polymerization. Design of radiation facilities to economically employ spent reactor fuel elements, composite or individually isolated fission products such as cesium 137, is one of the problems facing the design engineer in the nuclear field. 

As may be clear from Sections II and III, the proportions of the various fission product isotopes that might be released if there were a reactor accident, must depend to some extent on the type of reactor, the kind of accident that happens to it, its containment, and how safeguard devices perform. There is such a variety of reactors and such a plurality of failure modes, that one would be rash to attempt to make a single statement, however broad, intended to cover all such releases. Yet, if some coherent... 

As can be seen from the Gibbs partial free energies of formation shown in Fig. 3.14., the alkaline earths, the earth metals and the rare earth elements in contact with UO2 are stable as oxides. From these data it can be concluded that the fission product isotopes belonging to these elements are present in the fuel in their usual oxidation states or, in macrochemical expression, as double oxides with UO2. 

With regard to the fission product isotopes of Zr, Nb, Ru, Ce, Pr, La it can be assumed that they are not liberated directly from the fuel of a failed rod but that they are released by leaching of the fuel pellets and that the amount transported to the coolant is equivalent to the amount of fuel released from the defective rod. On the other hand, a direct release is assumed for strontium and barium, with the investigations suggesting a release rate lower by a factor of 10 than that of cesium (Beslu et al., 1984). 

At the PWR primary coolant pH of 7 to 8, the fission product isotopes of the tri- and tetravalent elements show strong hydrolysis, resulting in very low solubilities. This macrochemical behavior is consistent with the observations made in coolant analyses that these radionuclides can be almost quantitatively isolated together with the suspended corrosion products by filtration. However, this behavior does not necessarily indicate the presence of particular oxides or hydroxides of these fission products, since due to their very low element concentrations in the coolant their solubility limits are probably not exceeded. Presumably, these element traces are attached to the corrosion product oxides either by adsorption onto their surfaces or by formation of mixed crystals. A significant fraction of the longer-lived tri- and tetravalent fission products, as well as of the actinides, is incorporated into the contamination layers which cover the primary circuit surfaces. However, because of the usually very low actiAuty concentrations of these radionuclides in the coolant and, consequently, in the contamination layers, their contribution to the contamination dose rates is negligible. 

Studies of accelerator driven, or hybrid, reactors are now being made. These have a somce of neutrons in the core, produced by a proton beam striking a suitable target, the neutrons being produced in spallation reactions. These extra neutrons can help to improve the neutron economy, this being helpful for incineration of minor actinide and fission product isotopes. For these studies the reactions of interest and the energy ranges are wider than for conventional reactors. 

MA isotopes can be transmuted more efficiently in fast reactors than thermal because most have a lower ratio of capture to fission for fast neutrons. However, for the efficient transmutation of fission product isotopes a soft spectrum is required, so moderating assemblies situated around the core of a fast reactor are favoured. 

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